Method of forming metal ladder structures and the like



E. J. WILLIS June 18, 1968 METHOD OF FORMING METAL- LADDER STRUCTURES AND THE LIKE Filed Feb. 5, 1965 INVENTOR. EL 02/6 J WILL/5 AITGENEYS United States Patent;

3,388,454 METHOD OF FORMING METAL LADDER STRUCTURES AND THE LIKE Eidrich J. Willis, Bridgeville, Pm, assignor to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania Filed Feb. 5, 1965, Ser. No. 430,538 3 Claims. (Cl. 29-523) This invention relates to the mechanical joinder of metal elements and particularly to the joinder of metal rungs and stringers to form improved ladder type structures for climbing and support purposes.

In the fabrication of metal ladders, the interconnection between the rung and the stringer or side rail is critically determinative of the stiffness of the ladder both in racking and in shear. One expedient employed to increase ladder rigidity is to upset or bead the ladder rung both inside and outside of the stringer web in such manner as to effect a compressive interconnection between the upset beads and the web. Such fabrication is conventionally effected in two operations wherein the rung is initially headed and then located in the stringer holes on each side by hand after which the outer end of the rung is either spun over or upset by a die and the use of hydraulic force.

In the fabrication of ladders of the type herein of concern, the economies inherent in the effecting of a double upset type of interconnection at both ends of the rung member in one fabrication operation have been long apparent. Equally apparent, however, has been the fact that in the effecting of a double upset by a single stroke of the forming dies, the stringers themselves will be displaced as the rung metal is displaced to form the beads and therefore any contemplated fabrication of a multiple rung K straight ladder incorporating such interconnection would require that the stringers be held apart a predetermined distance each time a rung is upset in position and that such spacing would shift during the deformation operations. Although not insurmountable, the fabrication problems flowing from the incompatability of such requirements to the required length of the stringers and the rigidity necessarily inherent therein have effectively precluded the formation of a double upset type of interconnection by a single operation in the fabrication of metal ladders.

This invention may be briefly described as an improved method of producing a metal ladder of improved construction and which includes, in its broad aspects, the selective formation of a pair of upset beads in the rung on both sides of a rung receiving aperture in a stringer web of substantially planar character in one operation without stringer displacement by introduction of a conjoint deformation of the portion of the stringer web disposed adjacent to said aperture.

Among the advantages of the subject invention is the provision of a one step fabrication method for effecting a double upset interconnection between the rungs and stringer web of a metal ladder that is readily adaptable to automated operation to effect increased production at reduced cost. Still another advantage is the provision of a strong, simple and attractive connection between the rung and a ladder stringer that economically dispenses with auxiliary elements and is formed solely from the basic ladder components.

The primary object of this invention is the provision of an improved method of effecting a double upset interconnection of metal rungs to a stringer web in ladder fabrication. I

Other objects and advantages will become apparent to those skilled in this art from the following portions of this specification and from the appended drawings which 3,383,454 Patented June 18, 1968 "ice schematically show, by way of illustrative example, the sequenced positional disposition of the essentials of presently preferred apparatus for carrying out and effectuating the principles of the invention.

Referring to the drawings:

FIGURE 1 is a side elevation, partially in section, schematically illustrating the positional dispositions of the essentail apparatus elements prior to initiation of the deforming operations in the fabrication of a ladder from aluminum or its alloys.

FIGURE 2 is a side elevation, partially in section, illustrating the positional disposition of the apparatus elements at one end of the ladder rung at an intermediate stage of the deforming operations.

FIGURE 3 is a section on the line 3-3 of FIGURE 2.

FIGURE 4 is a schematic fragmentary section of the components illustrated in FIGURE 2 showing the positional disposition thereof at a succeeding stage in the deformation process.

FIGURE 5 is a schematic fragmentary section of the components illustrated in FIGURE 4 showing the positional disposition thereof at the completion of the deformation operation.

FIGURE 6 is a fragmentary view partially in section, showing the double upset interconnection of a ladder rung and stringer that results from the practice of the invention.

As indicated above, the drawings shown, in schematic form, only the essentails of suitable apparatus adapted for the fabrication of a ladder type structure, it being understood that such elements are included in auxiliary apparatus and jigs of conventional nature, for positioning and guiding the path of reciprocation of the various elements thereof, for inducing such movement and for introducing, positioning and displacing the workpieces during the fabrication operation.

Referring now to the drawings and initially to FIG- URE 1 there is provided a workpiece in the nature of a rung member 6 suitably in the form of a metal tube. The rung member 6 is supported by disposition of its terminal ends within complimentally sized rung receiving apertures 8, 10 in the web portions 12 and 14 respectively of a pair of side rail or stringer members disposed in spaced relation and substantially perpendicular to the longitudinal axis of said rung. As shown, the web portionslZ, 14 of the stringer members are preferably of a generally planar nature, at least in the area immediately surrounding the rung receiving apertures 8, 10 therein, while the overall cross sectional configuration of the stringer members, as is well known, may be U or I shaped or other suitable strength or rigidity producing configuration.

Disposed interiorly of the stringer webs 12, 14 and in abutting relationship with the interior faces thereof are a pair of displaceable gripper die assemblies generally designated 13 and 15 and including a first pair of opposed gripper die members 16 and 18 associated with the stringer web 12 and a second pair of opposed gripper die members 20 and 22 associated with the other stringer web 14.

As will become apparent the subject apparatus is adapted to effect the desired interconnection of the rung 6 to both stringer Webs 12 and 14 simultaneously. To this and the apparatus elements disposed at each end of the rung 6 are essentially duplicatively identical. For the purposes of brevity and convenience, the hereinafter following detailed description will be directed to the structure for effecting the interconnection of the rung 6 to the stringer web 12, with the understanding that such description is equally applicable to the structure for effecting the in terconnection of rung 6 to the stringer web 14.

As indicated by the arrows, the gripper die members 16, 18 are selectively displaceable in a path perpendicular to the longitudinal axis of the rung 6 into and out of gripping engagement with said rungs. Said die members conventionally include suitable alignment pins 24 and alignment pin receiving recesses 26 to assure, upon convergent displacement thereof, the desired matching conformity of the mating die faces when brought into gripping engagement with the rung member 6. As best shown in FIGURES 1 and 3 the surfaces of the gripper die members 16, 18 disposed in abutting facing relation to the stringer web 12 are shaped to conjointly provide a tapered bore 28 in the nature of a shallow truncated conical section dependently terminating in a shallow annular recess or bore 30 that is of a diameter greater than the diameter of the main rung member engaging bore 32 by the desired depth of the upset to be formed as hereinafter described.

As will now be apparent, displacement of the gripping die members 16, 18 into compressive gripping engagement with the rung 6, serves to form or define an annular conical bore about the rung member in abutting relation with the portion of the stringer web 12 disposed around the rung receiving aperture 8 therein, with a second or recessed annular bore 30 disposed remote from the aperture 8, surrounded by a pressure or stop surface 34 that is disposed in abutting relation with the stringer web 12 and prevents displacement thereof coaxially of said rung 6.

Operatively associated with the gripper die members 16, 18 as described above, is an elongate mandrel member 40 sized to fit closely within the end of the rung 6 and of a length to extend beyond the locus of the annular recess 30. The insertable length of the mandrel 40 may be determined by a shoulder 42 of a radial extent substantially equal to that of the wall thickness of the rung 6. The adjacent body portion 44 of the mandrel in turn terminates in a head portion 46 of markedly greater diameter. Mounted in surrounding relationship about the body portion 44 of the mandrel member 40 and in abutting relation with the head portion 44 thereof is an outer upset die member 40. The surface of the outer upset die member 48 disposed in facing relationship with stringer web 12 is provided with an annular protruding cone shaped segment 50 of a size and shape that complements that of the cone shaped recess 28 in the closed gripper die assembly and an annular upsetting recess 52 that dependently terminates in radial alignment with the aforementioned shoulder 42 on the mandrel member 40.

As is apparent the mandrel 40 and outer upset die member 48 are adapted to be separately or conjointly displaced coaxially of said rung 6 and toward and away from said stringer web 12.

In operation of the subject apparatus a workpiece is formed, either manually or automatically by the disposition of a pair of stringer webs 12, 14 in predetermined spaced and parallel aligned relation and by the introduction of a rung member 6 into the rung receiving apertures 8, therein as illustrated in FIGURE 1. With the basic elements of a ladder type structure so disposed, the gripper die members 16, 18 are displaced into converging compressive and gripping relationship about the rung member 6 immediately interiorly adjacent the stringer Web 12. When so disposed the gripper die members not only preclude all undesired longitudinal displacement of the portions of said rung 6 engaged thereby but additionally serve to prevent undesired displacement of all portions of the stringer web 12 other than the portion immediately surrounding the rung receiving aperture 8 therein that is positioned in facing relationship with the conically shaped core 28.

When the rung member 6 is so gripped and positioned, the mandrel member 40 with the outer upset die member 48 mounted thereon is introduced into the end of the rung member 6 and displaced coaxially of the rung member 6 toward the stringer web 12. Such intial displacement will continue unimpeded, save for the friction intermediate the mandrel and rung member, until the shoulder 42 engages the end of the rung member 6 as illustrated in Cir FIGURE 1. As shown in FIGURE 2, continued displacement of the mandrel and outer upset die member 48 toward the stringer web 12 will displace the end portion of the rung member 6 and effect progressive formation of a bead or upset 60 within the recess 52. As displacement of the mandrel 40 and outer upset die member 48 continues, the bead 66 will grow in volume to substantially fill the recess 52 by the time the apex of the conical protruding segment engages the surface of the stringer web 12, illustrated in FIGURE 4. Further dirplacement of the mandrel 40 and outer upset die member 48 effects a selective displacement of the portion 62 of the stringer web 12 disposed immediately surrounding the rung member receiving aperture 8 into the conically shaped bore or recess 28 and out of the plane of the remainder thereof which is fixedly positioned by the surrounding stop surface 34 of the gripper die members. Such continued displacement of the mandrel member 40 and outer upset die member 48 and continued displacement of the end portion of the rung member 6 also effects the conjoint formation of an interior bead or upset 64 within the annular recess 30 in the gripper die, as shown in FIGURE 5.

As the mandrel 40 and outer upset die member 48 reach their limit of displacement or closed position relative to the gripper die assembly, the upset bead material and 64 is coined into highly compressed engagement against both sides of the displaced portion 62 of the stringer web 12, to form the completed joint illustrated in FIGURE 5, after which the mandrel 40 upset die 48 and gripper dies 16 and 18 are retracted as indicated.

As now will be apparent to those skilled in this art, the resulting interconnection of the rung member and stringer will be of the type illustrated in FIGURE 6, and that such provides a simple strong and neat connection which dispenses with the need of all extra pieces of metal. As will also now be apparent, the subject method and apparatus readily permits the desired interconnection of both ends of the rung to the stringer web by a double upset in one operation without any displacement of the stringer web itself except for the portion immediately surrounding the rung member recessing aperture therein. Such novel mode of operation not only provides for a readily automated formation and prepositioning of the workpiece but also facilitates the automation of the entire fabrication operation to permit realization of the production economies inherent therein.

Having thus described my invention I claim:

1. In the fabrication of metallic ladder type structures by interconnection of stringer webs to the ends of tubular rung members, the steps of locating the terminal end of an undeformed tubular rung member in a rung member receiving aperture in a stringer web,

fixedly positioning the portion of said stringer web disposed in remote surrounding relation to said rung member receiving aperture therein relative to said rung member, selectively displacing the terminal end portion of said rung member relative to the remainder thereof to progressively form a first upset bead exteriorly of said rung member receiving aperture in said stringer web and a second upset bead interiorly of said stringer web and selectively displacing the portion of said stringer web disposed in immediate surrounding relation to said rung member receiving aperture therein relative to the remainder thereof conjointly with the formation of said second upset bead.

2. The method as set forth in claim 1 including the coining of said upset beads into compressive engagement with the displaced portion of said stringer web surrounding said rung member receiving aperture therein.

3. A method of interconnecting tubular rung members 5 6 and stringer webs in the fabrication of metal ladder type References Cited SIZI'UCUIIBS comprising the steps of UNITED ST P locating the terminal end of an undeformed tubular rung member in a rung member receiving aperture in 3004625 10/1961 Arnold 182-228 a stringer web, 5 3,181,651 5/1965 Larson 182228 fixedly positioning the portion of said stringer web dis- 2,667,688 2/ 1954 Wi 29 512 posed in remote surrounding relation to said rung 3 140 540 7/1964 Greenman member receiving aperture therein relative to said rung member, deforming the terminal end of said 3119435 1/1964 Greenman 29243'52 rung member to form a first integral bead exteriorly 10 3,177,570 4/1965 y et a1 29243-52 of said rung member receiving aperture, 1,447,520 3/ 1923 Schade 29-5 23 displacing said bead longitudinally of said rung mem- 2 273 025 3 1942 Sadoski 29 523 ber into compressive engagement with the surface 3,039,186 6/1962 Stoyer et 29 523 of said stringer member immediately surrounding the 3,168,938 2/1965 Shaver 29*523 rung member receiving aperture therein to effect con- 15 joint deformation of the said portion of said stringer FOREIGN PATENTS web disposed in immediate surroundin relation to said rung member receiving aperture therein and 8/19 Grcfat Bntam' forming a second integral bead in said rung member 04 9/19 swltzerland' interiorly of said rung receiving aperture in said 20 stringer web by continued deformation of the termi- CHARLIE MOON P'lmary Examiner nal end of said rung member. REINADO P. MACHADO, Examiner. 

1. IN THE FABRICATION OF METALLIC LADDER TYPE STRUCTURES BY INTERCONNECTION OF STRINGER WEBS TO THE ENDS OF TUBULAR RUNG MEMBERS, THE STEPS OF LOCATING THE TERMINAL END OF AN UNDEFORMED TUBULAR RUNG MEMBER IN A RUNG MEMBER RECEIVING APERTURE IN A STRINGER WEB, FIXEDLY POSITIONING THE PORTION OF SAID STRINGER WEB DISPOSED IN REMOTE SURROUNDING RELATION TO SAID RUNG MEMBER RECEIVING APERTURE THEREIN RELATIVE TO SAID RUNG MEMBER, SELECTIVELY DISPLACING THE TERMINAL END PORTION OF SAID RUNG MEMBER RELATIVE TO THE REMAINDER THEREOF TO PROGRESSIVELY FORM A FIRST UPSET BEAD EXTERIORLY OF SAID RUNG MEMBER RECEIVING APERTURE IN SAID STRINGER WEB AND A SECOND UPSET BEAD INTERIORLY OF SAID STRINGER WEB AND SELECTIVELY DISPLACING THE PORTION OF SAID STRINGER WEB DISPOSED IN IMMEDIATE SURROUNDING RELATION TO SAID RUNG MEMBER RECEIVING APERTURE THEREIN RELATIVE TO THE REMAINDER THEREOF CONJOINTLY WITH THE FORMATION OF SAID SECOND UPSET BEAD. 